This project involves study of the biology of the parasitic protozoa, Trichomonas vaginalis, Entamoeba histolytica and Giardia lamblia. The major emphasis for the past year has been on Trichomonas with colloborators Honigberg, Spence, Gupta and Frost. Our laboratory is in the process of evaluating virulence assays in newborn mice and tissue culture which results will be compared with an adult mouse assay (Honigberg) and with clinical and histopathological pictures in patients (Spence, Gupta) produced by a series of new isolates of T. vaginalis (Spence). We have investigated several properties of metronidazole-resistant strains of Trichomonas vaginalis: time-dose relationships, pH optima, and susceptibility to hexosamines (Mattern, Natovitz, Spence). Some of these studies have led to the successful management of 4 cases of drug-resistant Trichomonas at the Johns Hopkins Hospital (Spence, Mattern). A systematic laboratory study of induction of metronidazole resistance in T. vaginalis is currently underway to evaluate factors contributing to the induction of drug resistance.